The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Multi-module power supplies, for example uninterruptible power supply (“UPS”) systems, have multiple UPS's, typically referred to as a UPS module, and typically load share among the UPS modules. Load sharing is used to equalize the stress on each UPS module and to provide the maximum range of load increase while causing the minimum load change for any individual UPS module. Each UPS module of the multi-module UPS system is limited to operating within its thermal capability to prevent damage to its internal components. When the internal temperature of a module reaches a maximum, the UPS module is disconnected (e.g., shut down) from the load until the problem is resolved, such as a repair made. This will result in either loss of redundant UPS module and/or an increase in the load for the UPS modules remaining connected to the load.
FIG. 1 shows a basic block diagram of a prior art multi-module UPS system 100. While multi-module UPS system 100 is shown as having two UPS modules 102, it should be understood that multi-module UPS system 100 can have more than two UPS modules 102.
Each UPS module 102 includes input magnetics subsystem 104 (such as an input transformer), an output of which is coupled to an input of an AC/DC converter 106. The AC/DC converter 106 may typically be a rectifier having switched rectifying devices, such as SCR's, thyristors, MOSFETs or the like. An output of AC/DC converter 106 is coupled to an input of DC/AC converter 108 as is an output of a back-up power source 110. Back-up power source 110 can be a battery bank, flywheel, fuel cell, generator or the like that provides power in the event of interruption of input power to multi-module UPS system 100, such as from a electric power utility distribution system. DC/AC converter 108 may illustratively be an inverter. An output of the DC/AC converter 108 is coupled to an input of output magnetics subsystem 112, which may be an output transformer. An output of output magnetics subsystem 112 is coupled to an output of the multi-module UPS system 100, which provides power to a load. A bypass switch 114 may be coupled between the input of UPS module 102, such as the input of input magnetics subsystem 104, to the output of UPS module 102, such as the output of output magnetics subsystem 112. Temperature sensors 116 may be coupled to one or more of input magnetics subsystem 104, AC/DC converter 106, DC/AC converter 108 and output magnetics subsystem 112. Temperature sensors 116 may also be coupled to a controller 118 which controls UPS module 102. Controller 118 may be a programmable device such as a microcontroller, computer or the like. Preferably, temperature sensors 116 are coupled to the components 104, 106, 108 and 112 of every UPS module 102, as indicated in FIG. 1.
FIGS. 2A and 2B are basic schematic illustrations of load sharing in prior art multi-module UPS systems, such as multi-module UPS system 100. In FIG. 2A, each UPS module 102 of multi-module UPS system 100 has the same capacity, or per-unit rating (“pu-c”). The load on multi-module UPS system 100, referred to as the “system load,” in FIG. 2A is shared equally among the UPS modules 102. That is, each UPS module 102 supplies the same percentage of the system load. In FIG. 2B, two of the UPS modules 102 have a 1 pu-c and two have a 2 pu-c. The system load is shared proportionally among the UPS modules 102 based on their individual pu-c. That is, each UPS module 102 supplies proportionally a percentage of the system load based on its pu-c.
In multi-module UPS systems such as multi-module UPS system 100, the temperature of critical components, inlet air and exhaust air of each UPS module 102 are monitored to determine if that UPS module 102 is operating within an acceptable range of temperatures. If cooling is insufficient resulting in excessive temperature, an abnormal condition is alarmed and eventually the UPS module 102 is shut down. This can unnecessarily stress the remaining, operating UPS modules, provided the UPS module experiencing an excessive temperature can still be operated satisfactorily at some reduced power output level.